The demand for improved network coverage, improved capacity and increasing bandwidth for both voice and data services in wireless systems has led to continuous development of a number of radio access technologies (RATs) including, for example, wideband channel division multiple access (WCDMA) and long term evolution (LTE). WCDMA may support the simultaneous use of two high speed downlink packet access (HSDPA) downlink component carriers (2C-HSDPA). LTE may support simultaneous transmission and/or reception using the radio resources of a plurality of component carriers between a network node, for example between an evolved Node-B (eNodeB), and a wireless transmit/receive unit (WTRU) within the same transmission interval.
Some operators may deploy both WCDMA/high speed packet access (HSPA) and LTE in the same coverage areas, with LTE as a data enhancement overlay. LTE deployments may have a coverage that is similar to existing WCDMA/HSPA deployments, and multi-mode WTRUs, (e.g., supporting both WCDMA/HSPA and LTE accesses), may be widely deployed.
Spectrum is a costly resource and not all frequency bands may be available to all operators, although it may be expected that many operators may offer support for both HSPA and LTE services. Carrier aggregation scenarios may typically be limited to at most 2-3 component carriers per RAT for a given operator. In addition, legacy deployments may be maintained for a foreseeable future while LTE is being deployed, which may lead to a situation where operators may see periods of underutilization of radio resources, spectrum and capacity in one of their RATs.
Therefore, there is a need in the art for a WTRU to operate simultaneously on multiple frequencies, where the WTRU operates on at least one of the frequencies according to a different RAT.